A standard or distributed layer-2 virtual switch implemented in a virtualized computing device consists of ports connected to virtual network interfaces (VNICs) of virtual machines (VMs), referred to herein as switchports, and ports connected to physical network interfaces (PNICs), referred to herein as uplinks. In such a virtualized computing device, the VNICs, the virtual switch, and the PNICs have separate MTU (maximum transmission unit) configurations. Typically, the VNIC MTUs are configured to match the virtual network MTU requirements, and the PNIC MTUs are configured to match the physical network MTU requirements. In addition, the virtual switch MTU is configured to match the virtual and physical network MTU requirements. However, because the MTUs of the VNICs and the PNICs are separately configured, it is possible for the virtual switch MTU to become out-of-sync with the virtual or physical network MTU requirements.
Although the out-of-sync condition may lead to network traffic disruptions, it is generally not fatal. Connections between end points would still be allowed despite the MTU mismatches because handshake packets for establishing the connections contain no data and the MTU mismatches would not affect transmission and receipt of frames containing the handshake packets. Disruptions would occur, however, when the size of the frame is greater than the MTU of the receiving end point. When this occurs, the frame will be dropped at the receiving end point and the transmitting end point will repeatedly reduce the frame size and retransmit the frame until it receives acknowledgement of a successful transmission from the receiving end point.